The Russian GLONASS

http://www.glonass-ianc.rsa.ru/pls/htmldb/f?p=202:1:12061333542270124939
The Russians added needless complications when they selected a silly
time-scale for their system and decided to share the spreading codes
between satellites. GLONASS also consumes a lot more bandwidth.
However, this would be an excellent demonstration of an SDR's
adaptability, since a working software GPS receiver has all the
necessary components that a GLONASS receiver requires. One just
rearranges them differently. GALILEO falls into the same category.

Q&A

Q: What about DGPS for GPS positioning accuracy
improvement?

A: For the continental US, WAAS is more reasonable.
The marine DGPS beacons that operate at LF (~300kHz) would require
another RF path and related antenna.